Shelf-stable silane-modified aqueous dispersion polymers

ABSTRACT

Disclosed herein is a process for preparing a shelf-stable, one-pack, silane modified (meth)acrylic latex interpolymer composition, wherein the process comprises continuously adding at least a portion of a mixture comprising at least 0.5 mole percent of a vinyl silane comprising hydrolyzable groups and up to 99.5 mole percent of a (meth)acrylic monomer to water and a surfactant in a reaction vessel, wherein said addition is carried out in the presence of a polymerization initiator and buffer sufficient to maintain the pH of the reaction at a level of at least 6 throughout the reaction, while simultaneously hydrolyzing from about 10 to about 60% of the hydrolyzable groups of the vinyl silane.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to (meth)acrylic latex copolymers.As employed herein, the terminology “(meth)acrylic” is intended to mean“acrylic or methacrylic”. More particularly, the present inventionrelates to an aqueous (meth)acrylic latex copolymer, modified byincorporation of a vinyl silane bearing hydrolyzable groups, such asalkoxy groups, which cures at room temperature without added catalystafter application to a substrate to provide a crosslinked, solventresistant film or object, wherein said copolymer is stable for at leastone year at room temperature.

[0003] 2. Description of Related Art

[0004] There is extensive prior art on free radical copolymerization ofunsaturated silanes with organic comonomers, in solvent-borne systems aswell as in waterborne systems. Although not completely absent, shelflife problems and problems due to high levels of silane incorporationare not of overriding importance in non-aqueous systems. In waterbornesystems, most of the art ignores shelf life issues, or does not attemptto provide long shelf lives, particularly when higher concentrations ofsilanes are involved. For specialized applications, these systems can beused shortly after synthesis.

[0005] Aqueous dispersion polymers (commonly, latex, latexes, latices)are well known. Some general references include:

[0006]Waterborne and Solvent Based Acrylics and their End userApplications, ed. P. Oldring and P. Lam, Volume I of Surface CoatingsTechnology, John Wiley and Sons, New York, 1997, especially chapter II,and;

[0007]Resins for Surface Coatings, Volume 1, Acrylics and Epoxies, H.Coyard, P. Deligny and N. Tuck, John Wiley and Sons, New York, 2001.

[0008] In these references typical synthesis conditions, initiatortechniques, comonomers, end use properties and application conditionsare described.

[0009] Latexes can be provided with superior properties for use incoatings, sealants, and adhesives by incorporation of organofunctionalalkoxy silanes in the polymer. The superior properties includeresistance to common household chemicals and to solvents, as well asresistance of latex paints to scrubbing with household cleaning agents.In sealants, a sealant that can be obtained that produces joints thatare resistant to the environment, are flexible, and do not flow aftercuring in place. The properties arise from the crosslinking of thepolymer chains in the latex after application and flow out orcoalescence of the latex. Inclusion of silanes provides an effectivemechanism for creating “self-crosslinkable” latex polymers, which do notneed the addition of a separate crosslinking agent—that is, they are“one pack” systems, not “two pack” systems. There are also chemistriesthat do not involve silicon-containing comonomers that achieve some ofthe benefits of one pack, self-crosslinkable latex systems. Silicon(silane) based technologies offer superior resistance to degradation byUV light and the environment, compared to most other technologies.

[0010] This technology—based on alkoxysilane comonomers—has beenpracticed to some degree for years in a limited number of latexapplications. However, there are deficiencies in what has been achievedto date, particularly with regard to combining good stability and goodlow temperature cure.

[0011] First—alkoxy silanes are reactive with water. Hydrolysis of thealkoxy groups attached to silicon, such as methoxy or ethoxy groups,occurs readily and produces free alcohol, such as methanol or ethanol.Remaining on the silicon atom after hydrolysis is an —OH group, viz., asilanol. The condensation of two silanols to form an Si—O—Si bond, withthe release of water, is thermodynamically favored. Unfortunately,premature hydrolysis and condensation can destroy a silane and make asiloxane polymer of it before it has a chance to be incorporated into alatex in a uniform and well controlled fashion during polymerization.Hydrolysis and condensation after incorporation of the silane canprematurely crosslink the latex polymers during storage, resulting insolidification and gelation of the latex or latex-containing product inthe container. If the crosslinking occurs within the latexmicroparticles, gelation may not be apparent, but the particles will notflow together and will not coalesce after application. This can resultin reduced gloss (for coatings) or brittle films that have no integritywhen exposed to solvents, or sealants with poor integrity. On the otherhand, if this process can be controlled, a latex can be produced whichuses this chemistry to crosslink the polymer system after application,to give superior properties.

[0012] In some applications, it is possible to heat the substrate afterapplication of a silane-containing latex coating. The “stoving” orbaking of articles coated with paint is well known. This heat can beused to “activate” the silane chemistry described, provided thechemistry can be kept “latent” while the silane-modified polymer systemis stored on the shelf awaiting use. However, heating uses energy andsome substrates may not be able to withstand heating. Catalysts, such asacids, bases, and metallic compounds (tins, titanium derivatives, etc.)may be used to catalyze the reaction. This is normally accomplished byusing a two-pack system, which is less desirable than a one-pack system.Two-pack systems require control of the amount of additive, and may havevery limited “open life” or “pot life” after addition of the catalyticagent.

[0013] Thus, it is particularly desirable to have a one-pack system,which cures under ambient conditions after application, and which, atthe same time, does not prematurely react during storage. For practicaluse, a product such as a coating must be stable during storage for manymonths or years. This is an extremely difficult goal to achieve, owingto the conflicting needs of reactivity and stability. Any approach thatrelies on the use of an extremely unreactive silane that can survivestorage because of its low reactivity faces the problem of to how makethe unreactive silane become reactive on command. To achieve thiswithout heat or a catalyst is very difficult.

[0014] In some cases, the goal of shelf stability and room temperaturecure in a one-pack system can be achieved by using extremely lowconcentrations of silanes. The rate of condensation of two silanols toform a siloxane crosslink is proportional to the square of theconcentration of silanol groups. (The rate equation is second order insilanol concentration.) Thus, the condensation reaction can be slowed byreducing the silane concentration, and the effect is very strong becauseof the dependence on the square of the concentration. However, if onewishes to obtain a higher level of properties and faster cure of thesystem after application, it is desirable to increase the silaneconcentration above levels that are typically stable through the use ofvery low silane concentrations, i.e., above small fractions of oneweight percent in the polymer.

[0015] As can be seen from these comments, trying to control thechemistry occurring in a latex polymer system is not simple orstraightforward. Factors which can influence the results are:

[0016] 1. Temperature. Polymerizations are typically carried out atelevated temperatures, such as 60 to 65 degrees Celsius. Storage may beat room temperature. Application is usually at or near room temperature,but the applied coating may be heated.

[0017] 2. Water concentration. While water concentration is high in theaqueous phase—nearly 55 moles per liter—it will be much less in the oilphase. Hydrolysis and condensation rates are influenced by waterconcentration.

[0018] 3. Solubility. A hydrolyzed silane, carrying silanols, is muchmore water soluble than the unhydrolyzed silane. A vinyl silane has adifferent ratio of polar and non-polar groups than a silane with amethacryloxypropyl substituent on silicon.

[0019] 4. Chemical structure. Monomeric vinyl silanes tend to be morereactive to hydrolysis than silanes with the same alkoxy groups in whichthe silicon is not directly attached to a vinyl (unsaturated) group.Once polymerized into an organic copolymer, the alkoxy groups on siliconthat is derived from a vinyl silane, and that is, in turn, directly onthe polymer backbone, will have reduced reactivity due to stericshielding by the bulky polymer chain. The same factor reduces reactivityfor condensation as well as for hydrolysis. In comparison, the siliconderived from a methacryloxypropyl silane is several atoms away from thebackbone, and its chemistry is less influenced by steric factors.

[0020] 5. Environmental variables. Factors, such as pH and theconcentration of acidic or basic groups or metal ions and nucleophilesin the reactants, will influence the silane chemistry in different ways,depending on the type of silane, whether hydrolysis and/or condensationare being considered, and the like.

[0021] The complexity of these interactions makes it extremely difficultto predict the results of a synthesis before actually running thereaction and testing the results.

[0022] Commercially available silanes that can copolymerize by freeradical induced addition polymerization with acrylic and vinyl organiccomonomers, and that are available in sufficiently large productionquantities to be practical for large scale industrial use, are eithervinyl functional silanes or methacrylate functional silanes. An exampleof a vinyl functional silane is vinyltrimethoxysilane. An example of amethacrylate functional silane is methacryloxypropyltrimethoxysilane. Asa class, vinyl functional silanes are substantially less expensive perpound than methacrylate silanes. For large scale industrialapplications, therefore, the use of vinyl functional silanes ispreferred on a cost per alkoxy silane (or per silanol) group. In fact,both the lower cost per pound of vinyl silanes (relative to methacrylatesilanes) as well as their lower equivalent weight per alkoxy silanegroup, may be necessary to achieve a commercially viable andeconomically feasible technology. Owing to the selective nature of thereactivity of the double bond during copolymerization with vinyl andmethacrylic or acrylic monomers, vinyl silanes can copolymerize readilywith vinyl monomers, such as vinyl acetate. Vinyl monomers do notreadily copolymerize with (meth)acrylate double bonds and special careis required to achieve uniform incorporation of any vinyl monomer(whether it is a silane or not) into polymers consisting primarily ofmethacrylate or styrenic monomers. However, for many end uses, moreexpensive methacrylate or acrylate organic comonomers are preferred,because the resulting polymers have superior durabilty, weatherabilty,higher glass transition temperatures, and other superior properties,even in the absence of silane comonomers.

[0023] When considering the rate of reaction to incorporate the silaneinto the polymer, one must also consider the rate of hydrolysis of thesilane before and after incorporation in the latex polymer, as notedabove. In general, trialkoxyvinylsilanes hydrolyze more quickly than(meth)acryloxyalkyltrialkoxysilanes as free monomers. Once the silaneshave been incorporated into the polymer, the trialkoxy silane residuewill tend to be less reactive in hydrolysis and condensation because ofthe steric shielding arising from the location of the silicon directlyon the polymer backbone.

[0024] Thus, overall, the problem to be solved is how to achieve a shelfstable, one-pack, silane modified aqueous dispersion polymer (latex)system using vinyl silanes with (meth)acrylic organic comonomers, whileachieving silane concentrations well above 1% by weight, up to 5% oreven more, that will cure at room temperature to a solvent and chemicalresistant product, and that can be stored for at least six months and,preferably, over one year, without premature crosslinking to a degreesufficient to render them substantially useless for coatingsapplications.

[0025] U.K. Patent No. 1,407,827 discloses a process for the manufactureof stable coagulate-free aqueous vinyl dispersions having improvedadhesion. In this process, (i) (a) one or more monomers selected fromvinyl esters of carboxylic acids, acrylic acid esters, and methacrylicacid esters, and optionally up to 25% by weight (relative to the totalweight of component (i)) of one or more othersingly-olefinically-unsaturated water-insoluble monomers, or (b) amixture of styrene and up to 40% by weight (relative to the mixtue) ofbutadiene, is copolymerized with (ii) from 0.3 to 5% by weight (relativeto the total weight of component (i)) of a silicon compound of a givengeneral formula. Polymerization is carried out at a temperature withinthe range of from −15 to +100° C. in an aqueous phase, and in thepresence of a water-soluble free-radical initiator and an emulsifierand/or protective colloid.

[0026] U.S. Pat. No. 3,575,910 discloses silicone-acrylate copolymers,aqueous emulsions of these copolymers, latex paints containing thecopolymers and articles of manufacture having a coating containing thecopolymers.

[0027] U.S. Pat. No. 3,706,697 discloses that the aqueous emulsionpolymerization of acryloxyalkyl alkoxysilane, alkyl acrylic esters, andoptionally other vinyl monomers produces copolymers that are curable atlow temperatures. The silane may be introduced to the polymerizationafter a portion of the other monomers are polymerized. It is said thatheat curing improves the solvent resistance of cured as-cast films ofthe latex and that silanol curing catalysts enhance the cure rate.

[0028] U.S. Pat. Nos. 3,729,438 and 3,814,716 disclose latex polymerscomprising a dispersion of an interpolymer selected from the classconsisting of (A) a copolymer of vinyl acetate and vinyl hydrolyzablesilane and (B) a terpolymer of vinyl acetate, an ester, e.g., acrylicester, maleic ester or fumarate ester, and vinyl hydrolyzable silane, aswell as the crosslinked polymers derived therefrom. The latex polymersare said to have utility as protective surface coatings and as vehiclesfor paint formulations.

[0029] U.S. Pat. No. 4,716,194 discloses that the removability ofacrylate based pressure sensitive adhesives is substantially improved bythe addition thereto of a small amount of an organofunctional silanemonomer.

[0030] U.S. Pat. No. 5,214,095 discloses stable, aqueous emulsioncopolymers with controllable siloxane crosslinking functionality. Thesecopolymers are prepared by a concurrent free radical and cationicinitiated emulsion polymerization of at least one free radicalinitiatable monomer, at least one linear siloxane precursor monomer, andat least one bifunctional silane monomer having both free radicalpolymerizable and silicon functional groups. The copolymers are said tobe useful in curable coatings, paints, caulks, adhesives, non-woven andceramic compositions and as modifiers, processing aids and additives inthermoplastics, cements and asphalts.

[0031] U.S. Pat. No. 5,482,994 discloses polymer latices that arecompositions formed by adding an unsaturated alkoxy silane and aninitiator to a preformed emulsion polymer. The polymer latices are saidto have utility as protective surface coatings, adhesives, sealants andas vehicles for paint formulations.

[0032] U.S. Pat. No. 5,599,597 discloses unreinforced or reinforcedconcrete moldings, for example concrete pipes, with improved corrosionresistance to acids and acidic sewage, improved permeation resistance toinorganic and organic liquids and gases and improved mechanicalstability, produced by molding with machines, for example in pressmolding machines or extrusion machines or concrete pipe pressingmachines, and allowing to harden plastic-viscous concrete mixtures ofhydraulic inorganic binders, preferably cement, aggregates and water,where, in the preparation of the plastic-viscous concrete mixtures, tothe latter has been added in a positive mixer an effective amount of anaqueous plastics dispersion based on anionic and hydrolysis-resistantcopolymers of ethylenically unsaturated monomers, the minimum filmforming temperature (MFT) of which is above the setting temperature ofthe concrete mixture, preferably above 23° C.

[0033] U.S. Pat. No. 5,932,651 discloses emulsion copolymerizing aparticular crosslinker, i.e., either a siloxane or silazane, with anorganic monomer. An emulsion can be formed having particles consistingof polymer chains formed from organic monomer. Depending on thecrosslinker and reaction conditions, these emulsion polymer chains canbe either crosslinked or uncrosslinked. The uncrosslinked polymer chainscan be crosslinked at a later point by the addition of a suitablecatalyst.

[0034] U.S. Pat. No. 5,994,428 discloses storage-stable, silane-modifiedcore-shell copolymers comprising a shell-forming copolymer 1 of a) from70 to 95% by weight, based on the overall weight of the shell, ofacrylic and/or methacrylic C₁- to C₁₀-alkyl esters of which from 20 to80% by weight have a water solubility of not more than 2 g/l and from 80to 20% by weight, based in each case on the comonomers a), have a watersolubility of at least 10 g/l, and b) from 5 to 30% by weight, based onthe overall weight of the shell, of one or more ethylenicallyunsaturated, functional and water-soluble monomers including aproportion of from 25 to 100% by weight, based on the comonomers b), ofunsaturated carboxylic acids, and a core-forming copolymer II of one ormore monomers c) from the group of the vinyl esters, monoolefinicallyunsaturated mono- or dicarboxylic esters, vinylaromatic compounds,olefins, 1,3-dienes and vinyl halides, wherein the shell contains nosilane compounds and the core comprises one or more silane compounds d)from the group of the mercaptosilanes alone or in combination witholefinically unsaturated, hydrolyzable silicon compounds.

[0035] U.S. Pat. No. 6,130,287 discloses an emulsion polymer comprisinga protective colloid and a functionalized silane component which is of agiven structural formula.

[0036] WO 98/35994 discloses emulsion polymers that are said to have anexcellent combination of blocking resistance, water spotting resistanceand ethanol spotting resistance. These polymers are made from a monomermixture including a monomer with a highly polar group that includeseither a carboxylated or sulfonated monomer, or both, a monomer having ahydrolyzable silicone group, and a nonfunctional monomer that can beselected to provide a desired minimum film formation temperature. Thesepolymers are said to be useful in paint and coatings applications.

[0037] European Patent Publication No. 0 327 376 discloses copolymers ofvinyl esters and silicon monomers, with very low levels of the siliconmonomer, that are said to be especially suitable as binders for emulsionpaints, giving good scrub resistance. Vinyltrimethoxysilane iscopolymerized with organic comonomers comprising at least 40% vinylacetate. Substantial or full hydrolysis of the silanes to silanols isexpected. pH is not mentioned as a critical variable, and no pH rangesare indicated.

[0038] Bourne et al., J Coatings Technology, 54:69-82, #684, (January,1982) describe attempts to obtain stable silane-modified latexcopolymers from a variety of acrylate and methacrylate organic monomersby copolymerization with various methacrylate functional alkoxy silanes.These attempts met with failure. A range of pH conditions was attemptedwith ethyl acrylate as the comonomer. Conditions including starting atpH 9 or pH 7 and allowing the pH to drift, as well as pH 9 or no pHadjustment resulted in gelation (coagulation) during the reaction. Runsmade at pH 7 did not coagulate during synthesis. However, even thosepreparations gave unacceptable levels of coagulum and inadequate shelfstability.

[0039] Marcu et al., Macromolecules, 36:328-332 (2003) carried outextensive studies using extraordinary techniques in attempts to obtainstable silane modified emulsion polymers. These authors attempted tocopolymerize vinyltriethoxysilane with butyl acrylate. In order toobtain stable emulsion polymers, they had to resort to the use of a“mini-emulsion” technique. This technique involved addition ofhexadecane to the reaction mixture to form an oil phase that might“protect” the silane from hydrolysis, plus the use of ultrasound toachieve extremely high shear and agitation. pH control is mentioned asbeing prominent in the literature and is used in their work. Theexperiments were run using sodium bicarbonate buffer at one mole % onmonomers, at pH 6.5 (page 330, experimental section.) Even with thesetechniques, using the reaction scheme of batch reaction, they wereunable to get the silane to copolymerize by free radical additionpolymerization with the butyl acrylate. Instead, hydrolysis andcondensation reactions of the reactions of vinyltriethoxysilane producedsome form of oligomer, which eventually reacted with the organic latexpolymer, possibly by transesterification or some other heterolyticmechanism. Control reactions run without the oil phase were also run,and gave poor results.

[0040] Cooke et al., Emulsion Polymerization with Hindered SilaneMonomers, presented at Silicones in Coatings III, Barcelona, Spain, Mar.28-30, 2000, addresses the use of highly hindered silanes with reducedhydrolytic reactivity, such as vinyl-tri-isopropoxysilane andmethacryloxypropyl-tri-isopropoxysilane, with acrylate or methacrylatecomonomers. Further studies with this type of silane were reported inSilicones in Coatings IV, at Guildford, UK, May 30-31, 2002. In thiswork, the use of sodium bicarbonate buffer to control pH is describedand it is stated not to be necessary with the vinyl silanes, only withthe methacrylate silanes. This work does not involvevinyltriethoxysilane.

[0041] Many other publications and patents exist, related to theobjective of this work to a lesser degree than those cited above. Areview is presented in Silanes in Coatings Technology, published in TheJournal of the Oil and Colour Chemists' Association, 79:539-550(December, 1996). The large number of publications and patents since the1970's attests to the difficulty of this problem. Many give conflictingadvice about conditions, such as pH and reaction conditions, and manyinvolve other reagents, other comonomers, and the like, all of whichhave the potential to change the complex balance among hydrolysis,condensation, and free radical polymerization in a system with a waterphase and an oil phase.

[0042] The disclosures of the foregoing are incorporated herein byreference in their entirety.

SUMMARY OF THE INVENTION

[0043] In accordance with the present invention, there is provided an(meth)acrylic latex, modified with a vinyl silane, e.g.,vinyltriethoxysilane, under specified conditions by a novel process andsynthesized to a specific range of composition, that is stable tostorage up to three years at room temperature and provides self curinglatex systems that cure to solvent resistant films with no addedcatalyst or heat.

[0044] In one embodiment, the present invention is directed to acomposition that is an aqueous (meth)acrylic latex copolymer, modifiedby incorporation of a vinyl silane bearing hydrolyzable groups, such asalkoxy groups, that cures at room temperature without added catalystafter application to a substrate to provide a crosslinked, solventresistant film or object, and that is stable for at least one year atroom temperature. Preferably, the latex comprises at least about 10% andup to about 60% of the alkoxy groups derived from the vinylalkoxysilanehydrolyzed to release alcohol during the polymerization. Morepreferably, the vinyl silane is a vinyltrialkoxysilane, where the alkoxymoiety is ethoxy or n-propoxy.

[0045] In another embodiment, the present invention is directed to aprocess for making this latex that is broadly similar to known latexpolymerizations, but is unique in that a specific range of pH ismaintained during the polymerization, the preferred vinyl silane isvinyltriethoxysilane, and the silane concentration is up to 3 mole %,possibly as much as 5 mole %, and greater than 0.5 mole % relative toother monomers. This process deliberately hydrolyzes some of the alkoxysilane groups to release alcohol and form silanols, but does not producesuch a high level of silanols that the system becomes unstable and willnot survive shelf aging.

[0046] In contrast to known art, which describes pH control duringsynthesis of silane-containing latexes in many conflicting referenceswith many different polymer systems and silanes, and discusses avoidingsilane hydrolysis and/or condensation, in this invention silanereactions of hydrolysis and further silane reactions are controlled tospecific, desirable levels.

[0047] More particularly, the present invention is directed to a processfor preparing a shelf-stable, one-pack, silane modified (meth)acryliclatex interpolymer composition comprising continuously adding at least aportion of a mixture comprising at least 0.5 mole percent of a vinylsilane comprising hydrolyzable groups and up to 99.5 mole percent of a(meth)acrylic monomer to water and a surfactant in a reaction vessel,wherein said addition is carried out in the presence of a polymerizationinitiator and buffer sufficient to maintain the pH of the reaction at alevel of at least 6 throughout the reaction, while simultaneouslyhydrolyzing from about 10 to about 60% of the hydrolyzable groups of thevinyl silane.

[0048] In another embodiment, the present invention is directed to ashelf-stable, one-pack, silane modified (meth)acrylic latex interpolymercomposition prepared by a process comprising continuously adding atleast a portion of a mixture comprising at least 0.5 mole percent of avinyl silane comprising hydrolyzable groups and up to 99.5 mole percentof a (meth)acrylic monomer to water and a surfactant in a reactionvessel, wherein said addition is carried out in the presence of apolymerization initiator and buffer sufficient to maintain the pH of thereaction at a level of at least 6 throughout the reaction, whilesimultaneously hydrolyzing from about 10 to about 60% of thehydrolyzable groups of the vinyl silane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] The process of the present invention comprises the aqueouscopolymerization of acrylate monomers and a vinyl alkoxy silane underconditions that are similar to, but distinct from, the conventional.Continuous addition of silane along with the other comonomers,preferably from the very beginning of the reaction, is necessary toincorporate some of the vinyl silane in the polymer by free radicaladdition polymerization. If the vinyl silane is not added continuously,it will not copolymerize, and may form a separate siloxane copolymer,which may or may not be grafted or otherwise reacted with the organicpolymer during the course of the reaction. As another possibility, thevinyl double bonds may not react until all of the acrylate monomers havehydrolyzed. Meanwhile, the vinyl silanes may be hydrolyzing, to formcondensable silanols with unreacted vinyl groups, and, in turn, asiloxane condensate polymer or oligomer. This causes an undesirable andnon-uniform incorporation of silane, or, in some cases, may result in aphysical mixture of two materials—an organic polymer and a siloxanepolymer, which is undesirable.

[0050] Vinyl silanes that can be employed in the practice of the presentinvention include, but are not limited to, vinylalkoxysilanes,especially vinylalkoxysilanes where the alkyl moiety of the alkoxy groupis primary, e.g., vinyltriethoxysilane, vinylmethyldiethoxysilane,vinyl-tri-n-propoxysilane, vinyl-tri-(methoxyethoxy)silane, and thelike. Other vinyltri- and dialkoxy silanes may be used under somecircumstances, but control of the reaction to obtain the desired degreeof partial hydrolysis becomes more difficult. Silanes solely substitutedwith methoxy groups hydrolyze too readily and release toxic methanol.Most higher alkoxy silanes, i.e., above propoxy, hydrolyze too slowlyfor convenient use. Secondary alkoxysilanes, such asvinyl-tri-isoproxysilane, are definitely too unreactive, as are tertiaryalkoxysilanes. Butoxy silanes generally hydrolyze too slowly and causeundesirable odors from the butanols released. Vinyltriethoxysilane andvinylmethyldiethoxysilane are preferred. The most preferred silane isvinyltriethoxysilane.

[0051] A wide range of acrylic and methacrylic comonomers common in theart can be employed in the practice of the present invention. (Forreference, see Waterborne and Solvent Based Acrylics and their End userApplications and Resins for Surface Coatings, Volume I, Acrylics andEpoxies, supra, which also describe process details, optionalcomonomers, test methods, and conventional process methods that can beemployed.) Styrenic monomers may be included readily, as theycopolymerize easily with acrylic monomers, but not at levels sufficientto cause property deterioration. Styrenic materials, however, are strongabsorbers of UV light and may reduce durability to exterior exposure.Optionally, up to 20 weight percent of one or more vinyl organiccomonomers, such as vinyl acetate, vinyl propionate, or vinylneodecanoate (VEOVA™), may be added, but preferably at a level lowenough to produce no significant deterioration of the durabilityproperties of the final product. Still other comonomers can be includedto a small degree, if desired, as long as the system retains itssubstantially (meth)acrylic characteristics.

[0052] In the process of the present invention, a buffer, such as sodiumbicarbonate at a level of from about 0.4% up to about 0.7% of theaqueous phase, is used to keep the pH in the range above 6. Higher andlower levels of buffer may be used if higher or lower amounts of acidicor basic materials are present in the reaction. The reaction typicallystarts at a pH above 8, and after 15-20 minutes lowers to a range of 6to 7, where it is maintained as monomer is fed. Additional buffer may beadded during the reaction. If shelf stability is not necessary for agiven application, acceptable latexes can be produced in preparationsthat have a pH lower than these preferred levels.

[0053] During the reaction process, some of the vinyltrialkoxysilane,e.g., vinyltriethoxysilane, hydrolyzes, and the amount of alcoholreleased can be determined. The desired alcohol release is above 10%,but less than 60%, preferably 19% to 48%, and may vary somewhat with thesilane concentration and structure chosen.

[0054] The composition produced is an aqueous (meth)acrylic copolymer,in which at least 1 mole %, preferably 1 to 5 mole %, more preferably 3to 5 mole % (approx. 7 to 9 wt %, depending on the other comonomers) ofvinyltrialkoxysilane has been incorporated primarily bycopolymerization. In the examples described herein, with the particularcomonomers used, 3 mole % of vinyltriethoxysilane corresponds to 5.2weight %.

[0055] The composition may be further characterized by its ability toform a crosslinked solvent resistant film when applied to a metal paneland allowed to stand at room temperature for 7 days. The ability towithstand at least 75 MEK (methyl ethyl ketone) double rubs is onemeasure of satisfactory crosslinking. (This technique is described inASTM D 4752-87 and is well known to those of ordinary skill in thecoatings art.)

[0056] Initiation of polymerization in the working examples was by astandard method known as redox initiation. Thermal initiation or otherinitiation methods may be used. In the reactions of the examples, atemperature between 60 and 65 degrees Celsius, which is optimum for theredox initiator system used, was desired. Temperature is not narrowlycritical, and any temperature can be used at which initiation methodscan be used effectively.

EXAMPLES

[0057] I. Reagents and Materials

[0058] Methyl methacrylate (MMA)

[0059] Butyl acrylate (BA)

[0060] Methacrylic acid (MAA)

[0061] Vinyltriethoxysilane-Silquest® A-151 silane (CromptonCorporation, OSi Specialties Group.)

[0062] Sodium bicarbonate (NaHCO₃)

[0063] Ferrous sulfate (FeSO₄)

[0064] Sodium formaldehyde sulfoxylate (SFS)

[0065] Potassium persulfate (K₂S₂O₈)

[0066] t-Butyl hydroperoxide, 70 wt. % in water (t-BHPO-70)

[0067] IGEPAL® CA-897 (Rhodia)

[0068] Deionized water

[0069] Ammonium hydroxide

[0070] II. Apparatus

[0071] 800 mL jacketed reaction flask (for 300 grain preparations.)

[0072] Heating fluid circulator

[0073] Thermometer

[0074] Overhead Stirrer

[0075] Metering pump for monomer solution (FMI piston pump RP-G400)

[0076] Syringe pump for initiator solutions (Syringe infusion pump 22,from Harvard Apparatus)

[0077] III. Formulation (Based on 300 Gram Total)

[0078] A. Water, Optional Buffer (Sodium Bicarbonate), Surfactant(s):

[0079] Deionized Water: 150 g

[0080] Sodium Bicarbonate buffer varied amounts

[0081] IGEPAL CA-987 13.5 g

[0082] B. Monomers

[0083] Monomers were chosen in these particular examples to keep aconstant percentage of MAA, and a constant ratio of MMA to BA, as silanecontent was varied. There is no limitation implied on the process. Foreach 100 grams of monomers, the following ratios were used, presented toallow percent amounts to be seen easily. As the syntheses all used 125grams of monomer, the weight amounts are to be multiplied by 1.25 tocalculate the amount of monomer charged in the working examples. Forexample, for a 3 mole % silane incorporation, the amounts of monomersused would be 6.50 grams of vinyltriethoxysilane, 38.50 grams of BA,78.125 grams of MA, and 1.875 grams of MAA. Mole (Weight) Percent SilaneDesired in Copolymer 0% (0.0%) 1% (1.73%) 2% (3.5%) 3% (5.2%)Vinyltriethoxysilane   0 g 1.75 g  3.5 g  5.2 g BA 32.5 g 31.9 g 31.5 g30.8 g MMA 66.0 g 64.8 g 63.6 g 62.5 g MAA  1.5 g  1.5 g  1.5 g  1.5 gTotal  100 g  100 g  100 g  100 g

[0084] C. Initiators:

[0085] FeSO₄ (0.15%, in water) 1.20 g

[0086] K₂S₂O₈ (solid) 0.9 g

[0087] SFS (2%, in water) 9.0 g

[0088] t-BHPO-70 0.1 g

[0089] Note: All initiator solutions should be freshly prepared prior touse.

[0090] IV. Synthesis

[0091] 1. 150 mL of deionized water were added to an 800 mL jacketedreaction flask, and 13.5 grains of surfactant and the indicated amountof sodium bicarbonate were added with gentle stirring. The contents wereheated to 63° C. with constant temperature fluid in the jacket whilepurging the flask with N₂. The N₂ blanket was maintained throughout therun.

[0092] 2. The silane and acrylic monomers (125.2 grams total) were mixedand transferred to a separate addition funnel.

[0093] 3. Initiator was added, FeSO₄ (1.2 grams, 0.15% aq) followed byK₂S₂O₈ (0.9 g), with agitation to the surfactant solution prepared inStep 1. Stirring was continued for 5 minutes.

[0094] 4. The first portion of monomer was added to the flask. Tenpercent of the monomer mixture prepared in Step 2 (12.5 grams) and 10%of the SFS solution (0.9 gram) were added to the reaction flask via twoseparate pumps over a period of about one minute. An exotherm wasusually noted. The reaction was allowed to run at a temperature of 65°C. for 15 minutes maintaining good agitation. The reaction temperaturewas maintained within 2-3 degrees of 65° C. for steps 5-7.

[0095] 5. The remainder of monomer mixture (112.7 grains) and anadditional 70% of the SFS solution (10.5 grams) were fed continuouslythrough separate pumps over a period of three hours. Sometimes a slightviscosity increase was noted.

[0096] 6. The reaction mixture was allowed to stir for another 30minutes after the monomers and this portion of initiator were completelyadded.

[0097] 7. At that point, the t-BHPO-70 (0.01 grain), followed by theremaining SFS solution (1.8 grains) were added over a period of 30minutes.

[0098] 8. The latex was allowed to cool to room temperature. The pH wasadjusted to 7.5 using ammonium hydroxide solution (<10% aq). The latexwas filtered using a 200 mesh nylon screen.

[0099] V. Application

[0100] A suitable coalescent system for the silylated latexes has beenfound to be 2% dipropylene glycol butyl ether plus 4%2-(2-butoxyethoxy)ethyl acetate based on the total weight of the latexincluding water. The formulation can be drawn down on zincphosphate-treated steel or thermoplastics (for making a free film) to adry thickness of about 1 mil (25 μm) and cured at ambient conditions orat elevated temperature, for various times.

[0101] Freshly synthesized latexes were allowed to remain at roomtemperature for at least 24 hours, usually 2 to 3 days, and never morethan 7 days before the samples were taken for “unaged” testing.

[0102] A small sample of latex was mixed with 2% dipropylene glycolbutyl ether containing 4% 2-(2-butoxyethoxy)ethyl acetate based on thetotal weight of the latex including water. It was allowed to stand for30 minutes. It was drawn down on a phosphated steel panel to give a dryfilm thickness of approximately 1 mil film by using wire-wound rod,number 24 (from The Gardner Company.) This coating rod gives a wet filmthickness of approximately 2.5 mil.

[0103] Coating films were tested after they were cured at ambientcondition for a certain time—usually 7 days and 30 or 40 days. In somecases they were baked at 120° C. for 20 minutes before testing or beforefurther ambient cure then testing. Baking can represent some end useconditions where heat is acceptable, and it also causes faster curing(formation of a crosslinked polymer network) than ambient curing. Thisis useful for an understanding of theoretical limits of whether and howmuch a system can cure with the ambient temperature limitation removed.

[0104] VI. Characterization of Silylated Acrylic Latexes and Propertiesof Coatings

[0105] Gel content: An accurately weighed (±0.1 mg) sample of coatingfilms was placed in a fine wire cage in a Soxhlet extractor, andextracted with refluxing acetone for 8 hours. The loss of weight fromthe coating sample was measured accurately, with the gel contentcalculated according to:

Gel Content (%)=(1−ΔW/W ₀)×100

[0106] where:

[0107] W₀ is the initial weight of coating sample, and

[0108] ΔW is the weight lost during solvent extraction.

[0109] If the film was brittle and fragmented into small pieces, as withover-crosslinked films, gel content could not be measured because thefilm was incompletely retained by the mesh. This procedure is based onASTM D2765-95.

[0110] MEK resistance: Double rubs according to ASTM D 4752-87, modifiedto continue rubbing until the substrate was exposed, even if the numberof double rubs was greater than the value of 50 as specified in the ASTMmethod.

[0111] Spot tests: This test was performed according to ISO 2812-1974. Aone inch square piece of filter paper was placed on the film. Eightdrops of solvent was added and the film was covered with a watch glass.In the case of acetone tests, the watch glass was removed after twominutes and the film wiped with a soft tissue paper. The result wasrated from 1 to 5, with 1 being complete removal, 2 having substantialspots removed, and 5 being no effect. In the case of MEK, the watchglass was removed after 30 minutes and the specimen observed withoutwiping.

[0112] Measurement of alcohol of hydrolysis released during the latexsynthesis or after completion of synthesis: A trap-to-trap (T-T)distillation apparatus was employed to separate the latex solids fromthe volatile components. The apparatus consisted of a 250 mL flask, areceiving tube, and connecting U-tube with a stopcock outlet at the bendof the U-tube. Sample size used was 7 to 10 grains, typically 8 grams.The distillation procedure included 4 major steps:

[0113] 1. Pre-freeze: The sample was frozen by rotating the sealedsample flask in dry ice. A frozen thin coating (shell) of sample on theflask wall was formed that ensured efficient vapor flow from sample tocondenser during the subsequent distillation. This markedly speeds upthe distillation owing to the higher surface area of the frozen latex.

[0114] 2. Deep freeze: The sample flask was attached to the distillationapparatus, and the sample flask was partly immersed in liquid nitrogento cool it further in preparation for the trap-to-trap distillation. Thesystem was sealed to outside air during this procedure.

[0115] 3. Vacuum: The distillation system was evacuated with amechanical pump to a pressure of approximately 0.05 mm Hg while thesample was maintained at liquid nitrogen temperature.

[0116] 4. Distillation: The system was closed (under full vacuum) andthe liquid nitrogen bath was removed from the sample flask and moved tothe receiving tube. As the sample slowly warned, volatiles evaporatedand condensed in the cold receiving tube. The distillation wasconsidered complete when the sample was a dry, white powdery solid.

[0117] A gas chromatograph (Hewlett Packard 5890 series II) equippedwith a capillary column packed with crosslinked phenyl/methyl siloxane(DB5, Agilent) and FID detector was used to analyze the distillatesamples. GC-MS spectrometric techniques were used to identify theseparated species. To determine quantitatively the content of alcohol inliquid distillate samples, a weighed amount of 2,4-dioxane was added asinternal standard after the distillation was complete.

Examples 1, 2, 3, and 4

[0118] Data from examples 1 through 11 and comparative example 1 areprovided in Table 1.

[0119] Latexes were prepared according to the general procedure, using 2mole % vinyltriethoxysilane, and the indicated amount of buffer.

Example 1a and 1b

[0120] This preparation was carried out in duplicate. It involved nobuffer, and the pH during the reaction was allowed to drift downwardfrom an initial pH of 4-5, rapidly decreasing within 15 minutes to lessthan pH 3 for the 3.5 additional hours of reaction time.

Example 2

[0121] This preparation used 0.2 gram of sodium bicarbonate buffer(0.13% in the water phase.) The pH during reaction was allowed to driftdownward from an initial pH of 8.5, rapidly decreasing within 15 minutesto pH 6.5 to 7, and further decreasing steadily to pH 2-3 at the end ofthe reaction.

Examples 3a and 3b

[0122] These duplicate preparations used 0.25 gram of sodium bicarbonatebuffer (0.17% in the water phase.) The pH during the reaction wasallowed to drift downward from an initial pH of 8.5, rapidly decreasingwithin 15 minutes to pH 6.5 to 7, and further decreasing steadily to pH3.5 (3a) and 4 to 5 (3b) at the end of the reaction.

Example 4

[0123] This preparation used 1.0 gram of sodium bicarbonate buffer(0.67% in the water phase.) The pH during reaction was allowed to driftdownward from an initial pH of 8.5, slightly decreasing within 15minutes to pH 8 to 8.5, and further decreasing steadily to pH 6.5 at theend of the reaction.

[0124] Examples 1a and b showed acceptable performance in the initialtests within a week of preparation. However, after one year of shelfstorage, performance deteriorated substantially.

[0125] Example 2 gave acceptable performance in the as-made tests, butshowed notable deterioration after one year.

[0126] Examples 3 (a and b) and 4 gave excellent performance as made andafter one year. After one year, the slightly better initial performanceof Example 3 had decreased and the performance of Example 4 was equal orhigher. At 2 mole % (3.5 wt. %) vinyltriethoxysilane, avoidance of theextreme lows of pH during reaction is sufficient to obtain acceptablestorage for one year at room temperature.

Examples 5, 6, 7, and 8

[0127] Latexes were prepared according to the general procedure, using 3mole % vinyltriethoxysilane, and the indicated amount of buffer.

Example 5

[0128] This preparation was carried out with no buffer, and the pHduring reaction was allowed to drift downward from an initial pH of 4,rapidly decreasing within 15 minutes to less than pH 3 for the 3.5additional hours of reaction time.

Example 6

[0129] This preparation used 0.15 gram of sodium bicarbonate buffer(0.10% in the water phase.) The pH during the reaction was allowed todrift downward from an initial pH of 8.5, rapidly decreasing within 15minutes to pH 6.5, and further decreasing steadily to pH 2-3 at the endof the reaction.

Example 7

[0130] This preparation used 0.2 gram of sodium bicarbonate buffer(0.13% in the water phase.) The pH during the reaction was allowed todrift downward from an initial pH of 8.5, rapidly decreasing within 15minutes to pH 5.5 to 6, and further decreasing steadily to pH 2-3 at theend of the reaction.

Example 8

[0131] This preparation used 0.5 gram of sodium bicarbonate buffer(0.33% in the water phase.) at the beginning. The pH during the reactionwas allowed to drift downward from an initial pH of 9, decreasing within15 minutes to pH 8, and further decreasing steadily to pH 5.5-5 at theend of three hours of monomer addition. An additional 0.3 gram of bufferwas added at that point and the pH was 7-7.5 until the end of thereaction. Total buffer was 0.8 gram, 0.53% in the aqueous phase.

[0132] Under the more stringent conditions of higher silaneconcentration (3 mole % vs. 2 mole %), the ability of systems thatfinished their reaction at substantially acidic pH's to provide goodshelf life and good performance in room temperature cure testing wasdiminished when compared to the samples made with 2 mole % silane. Sincethe rate of silanol condensation is proportional to the square of theconcentration of silanol groups, the rate of premature crosslinkingunder storage (all other things being equal) would increase by the ratioof 9 (i.e., 3 squared) to 4 (i.e., 2 squared), i.e., 225%. While Example5 was clearly inferior at both as-made and one year tests, examples 6,7, and 8 were all acceptable in “as made” testing. It is interesting tonote that allowing panels to cure for 30, 40, or 50 days at ambientconditions gave much better solvent resistance for Example 8 than forExamples 6 and 7. After one year, Example 8 was clearly superior toexamples 5, 6, and 7.

Examples 9 and 10

[0133] Latexes were prepared according to the general procedure, using 3mole % vinyltriethoxysilane, and the indicated amount of buffer. Example10 was prepared in duplicate, as 10a and 10b.

Example 9

[0134] This preparation was carried out with no buffer, and the pHduring the reaction was allowed to drift downward from an initial pH of1.64. After 15 minutes the pH was 1.54 to 1.69. After one hour ofmonomer addition, the pH was 1.26, and it remained strongly acidic overthe remainder of the reaction.

Examples 10a and 10b

[0135] These duplicate preparations used 0.65 gram of sodium bicarbonatebuffer (0.43% in the water phase.) The pH during reaction was allowed todrift downward from an initial pH of 9, rapidly decreasing within 15minutes to pH 6.5, and holding at 6 to 6.5 for the remainder of thereaction.

[0136] Room temperature tests were not carried out on these samples asmade or at one year of storage. After 21 months of storage, 10 and 10bshowed substantial superiority on MEK rub tests. At 33 months ofstorage, the superiority was still clear, even though the films ofExamples 10a and b were brittle and fragmented in the gel test. At least21 months shelf life was obtained.

Example 11

[0137] A latex was prepared according to the general procedure, usingonly 0.5% vinyltriethoxysilane, and no buffer. The pH profile was notmeasured, but was similar to that of examples 1, 4, and 9, since thesame procedure was followed. The reaction mixture was substantiallyacidic.

[0138] Data were taken on Example 11 as made and after 30 months. Thelatex was not overly crosslinked at 30 months, as evidenced by acoherent sample after extraction, but showed only 49% gel and only 50MEK rubs after 7 days at ambient.

[0139] The as-made sample also showed poor solvent resistance at 7 days:only 15 MEK rubs and 2 to 3 on the MEK spot test. These results showthat stable systems can be produced, albeit with lower properties, byreducing the amount of silane. This property set may be sufficient forsome applications, but the cured film is not substantially resistant tosolvents. Not enough silane was incorporated.

Comparative Example 1

[0140] A latex was prepared with no buffer and no silane. “As made”testing showed only 10 MEK rubs after 7 days at ambient, and spot testresults were only 1 for acetone and MEK tests at 7 days. Aged sampleswere not tested, but no change in values is expected, because no“self-crosslinking” chemistry mechanism is built into the latex. TABLE 1Data on Preparation and Testing of Examples 1 Through 11 and ComparativeExample 1 Table 1A-A Buffer Buffer Working Composition NaHC03 NaHC03 pHprofile - pH measured at time tin minutes Example mole % of wt. % ingrams in t = 200 to % ROH Coagulum Number silane water phase water phaset = 5 t = 20 t = 80 t = 140 t = 200 260+ released wt % Comp 1 No Silane0 0  1a   2% A-151 0 0 4-5 3-2 2-3 — — — 2%  1b   2% A-151 0 0 3.0 2-3 —— — 41% 2% 2   2% A-151 0.13 0.2 8.5 6.5-7     5-4.5 4.0 2-3 2-3 3%  3a  2% A-151 0.17 0.25 8.5 6.5-7   5.0 5.0 5-4   4-3.5 3%  3b   2% A-1510.17 0.25 8.5 7.0 5.5 5.5-5.0 5.0 5-4 1% 4   2% A-151 0.67 1.0 8.5  8-8.5   7-7.5 6.5-7   6.5 6.5 29% 3% 5   3% A-151 0 0 4 3   <3 — — —62% 4% 7   3% A-151 0.13 0.2 8.5 5.5-6   5 4   3   2-3 2% 6   3% A-1510.10 0.15   8-8.5 6.5 5 4.0 2-3 2-3 48% 1% 8   3% A-151 0.53 0.5 then+0.3 9 8   6.5-6   6   5.5-5     7-7.5 29% 2% 9   3% A-151 0 0 1.64 154-1.69 1.26 — — — 3% 10a   3% A-151 0.43 0.65 9 6.5 6-6.5 6   6    6-6.5 2% 10b   3% A-151 0.43 0.65 8.6-9.0 7.0-8.2 8.1-5.4 5.4 5.6 6.31% 11 0.5% A-151 0 0 1% Table 1A-B Room Temperature Cure Data on FreshLatex Preparations Working spot test Example age of SAL MEK Rubs MEKRubs MEK Rubs acetone, MEK, get content Number months baking 7 day 30day 40 day 7 day 7 day % Comp 1 0 none 10 1 1  1a 0 none 80 500 4 4 80.4 1b 0 none 80  200* 4 4 83 2 0 none 70 4-5 4-5 79.8  3a 0 none 50 4-5 471.2  3b 0 none 40 5 5 69.2 4 0 none 90 4 4 71.9 5 0 none 60 60  60 41,3-4   83.9 7 0 none 70 140 200 4-5 4 82 6 0 none 85 220 230 4-5 4-581.9 8 0 none 100 400 650 4-5 4-5 76 9 0 none No Data 10a 0 none 10b 0none 11  0 none 15 2-3 56.6 *Fifty days, not forty days. Table 1A-C RoomTemperature Cure Data on 12 Months Old Latex Preparations Working spottest Example age of SAL MEK rubs acetone, Number months baking 7 day 7day MEK, 7 day get content % Comp 1 10 none 11 1 1  1a 12 none 10 3-4 3(brittle)  1b 12 none 18 4 3-4 92.4 (brittle) 2 12 none 40 4 4 94.6  3a12 none 90 4 4-5 94.7  3b 12 none 130 4 4-5 97.5 4 12 none 110 4 4-594.5 5 11 none 16 3 1 (brittle) 7 11 none 40 4 4 (brittle) 6 11 none 404 4-5 (brittle) 8 11 none 130 4 4-5 95   9 10a 10b 11  Table 1A-D RoomTemperature Cure Data on 21 Months Old Latex Preparations MEK rubsWorking Example Number age of SAL months baking 2 day 7 day 30 day 40day Comp 1  1a  1b 2  3a  3b 4 5 7 6 8 9 21 none 10 150 10a 21 none 210350 10b 21 none 120 350 11  Table 1A-E Room Temperature Cure Data on 33Months Old Latex Preparations Working gel Example age of MEK rubs spottest content Number SAL months baking 2 day 7 day acetone, 1 dayacetone, 7 day MEK, 7 day % Note Comp 1  1a  1b 2  3a  3b 4 5 7 6 8 9 33none  7 11 1 3 1 (brittle) viscous  10a 33 none 30 130  4 4-5 4(brittle) viscous  10b 33 very viscous 11  30 none 50 4-5 5 49 Table1B-A gel content of age of coating, % MEK rub spot test latex baked at120° C., 120° C. MEK, acetone, Composition buffer months 20 min. bakedRT baked baked MEK, RT acetone, RT Acrylic latex 0 0 — 10 6 1 1 1 1 (nosilane) Acrylic latex 0 0 — 20 (no silane) Table 1B-B gel content ofcoating, % MEK rub Composition buffer age of latex months baked at 120°C., 20 min. 120° C. baked Acrylic latex 0 (no silane) Acrylic latex 0 20 7 (no silane) Table 1B-C age of latex gel content of MEK rub spot testComposition buffer months coating, % 120° C. baked RT MEK, bakedacetone, baked MEK, RT acetone, RT Acrylic latex 0 10 — 12 11 1 1 1 1(no silane) Acrylic latex 0 13 —  7 1 1 (no silane)

Examples 12 and 13

[0141] The above Examples 1 through 10 indicate that excessivehydrolysis of the alkoxy silane to release alcohol during the latexpreparation produces a latex that may be acceptable as made, but thatdeteriorates in storage, probably by excessive premature crosslinking.However, if the silane does not hydrolyze at all during the latexpreparation, properties will develop much too slowly, if at all, uponapplication. These examples were synthesized using a different vinylsilane, vinyl tri-isopropoxysilane, which allows much less hydrolysisbecause of its structure. While not perfectly comparable in all ways toExamples 1 through 10, the data do provide a strong indication thatthere is a lower limit to the amount of hydrolysis that must occurduring synthesis. In particular, a film cast at room temperature thathas cured to only 4% gel gives poor properties, and corresponds tohydrolysis of only 19% of the available alcohol. Even after baking toforce the cure, the 65% gel was soft, indicating poor crosslinking.

Example 12

[0142] A latex was prepared according to the general procedure, using 3mole % vinyl tri-iso-propoxysilane, instead of vinyltriethoxysilane, andno buffer. The pH profile was not measured, but was similar to that ofexamples 1, 4, and 9, since the same procedure was followed. Thereaction mixture was substantially acidic.

Example 13

[0143] This preparation also employed vinyl tri-iso-propoxysilane andused 0.22 gram of sodium bicarbonate buffer (0.15%) in the water phase.The pH during the reaction was allowed to drift downward from an initialpH of 8.5, rapidly decreasing within 15 minutes to pH 6.5, and furtherdecreasing steadily to pH 2-3 at the end of the reaction. Poorperformance at room temperature was improved by baking, but MEK rubtests were only acceptable even after baking. Example 12, more fillyhydrolyzed, cures at room temperature and gives good properties whenbaked. TABLE 2 Correlation of Degree of Hydrolysis with Properties ofCured Acrylic Latex Modified with Vinyl Silanes Gel content of BufferHydrolyzed coating film, % MEK rubs Example Grams and % in silane inlatex, Baked at 120° C., 120° C., Number water phase % 20 min. R.T curebaked 5 none 62 (too brittle to 84 900 have film) 6 0.15 g, 0.1%  48 8882 1000 8  0.8 g; 0.53% 29 87 80 600 12 none 63 88 84 350 13 0.22 g,0.15% 19  65*  4* 60

[0144] These data suggest that an acceptable range of hydrolysis forlatexes of this general composition and with a vinyl silane as thesilane component require more than 19% hydrolysis to provide acceptableproperties in room temperature cure. The upper limit is less clear fromthe data, but for vinyltriethoxysilane-containing materials, it is lessthan approximately 62% (Example 5).

[0145] In view of the many changes and modifications that can be madewithout departing from principles underlying the invention, referenceshould be made to the appended claims for an understanding of the scopeof the protection to be afforded the invention.

What is claimed is:
 1. A process for preparing a shelf-stable, one-pack,silane modified (meth)acrylic latex interpolymer composition comprisingcontinuously adding at least a portion of a mixture comprising at least0.5 mole percent of a vinyl silane comprising hydrolyzable groups and upto 99.5 mole percent of a (meth)acrylic monomer to water and asurfactant in a reaction vessel, wherein said addition is carried out inthe presence of a polymerization initiator and buffer sufficient tomaintain the pH of the reaction at a level of at least 6 throughout thereaction, while simultaneously hydrolyzing from about 10 to about 60% ofthe hydrolyzable groups of the vinyl silane.
 2. The process of claim 1wherein the vinyl silane comprising hydrolyzable groups is avinylalkoxysilane.
 3. The process of claim 2 wherein thevinylalkoxysilane is selected from the group consisting ofvinyltriethoxysilane and vinylmethyldiethoxysilane.
 4. The process ofclaim 3 wherein the vinylalkoxysilane is vinyltriethoxysilane.
 5. Theprocess of claim 1 wherein the (meth)acrylic monomer is selected fromthe group consisting of methyl methacrylate, butyl acrylate, methacrylicacid, and mixtures thereof.
 6. The process of claim 1 wherein the bufferis sodium bicarbonate.
 7. The process of claim 6 wherein the buffer isemployed at a level of from about 0.4% to about 0.7% of the aqueousphase.
 8. The process of claim 1 wherein the mixture further comprisesup to about 20 weight percent of at least one vinyl organic polymer. 9.The process of claim 8 wherein at least one vinyl organic polymer isvinyl acetate.
 10. A shelf-stable, one-pack, silane modified(meth)acrylic latex interpolymer composition prepared by a processcomprising continuously adding at least a portion of a mixturecomprising at least 0.5 mole percent of a vinyl silane comprisinghydrolyzable groups and up to 99.5 mole percent of a (meth)acrylicmonomer to water and a surfactant in a reaction vessel, wherein saidaddition is carried out in the presence of a polymerization initiatorand buffer sufficient to maintain the pH of the reaction at a level ofat least 6 throughout the reaction, while simultaneously hydrolyzingfrom about 10 to about 60% of the hydrolyzable groups of the vinylsilane.
 11. The composition of claim 10 wherein the vinyl silanecomprising hydrolyzable groups is a vinylalkoxysilane.
 12. Thecomposition of claim 11 wherein the vinylalkoxysilane is selected fromthe group consisting of vinyltriethoxysilane andvinylmethyldiethoxysilane.
 13. The composition of claim 10 wherein the(meth)acrylic monomer is selected from the group consisting of methylmethacrylate, butyl acrylate, methacrylic acid, and mixtures thereof.14. The composition of claim 10 wherein the buffer is sodiumbicarbonate.
 15. The composition of claim 14 wherein the buffer isemployed at a level of from about 0.4% to about 0.7% of the aqueousphase.
 16. The composition of claim 10 wherein the mixture furthercomprises up to about 20 weight percent of at least one vinyl organicpolymer.
 17. The composition of claim 16 wherein at least one vinylorganic polymer is vinyl acetate.
 18. An interpolymer compositioncomprising: A) at least about 0.5 mole percent of a vinylalkoxysilanemoiety in which from about 10 to about 60% of the alkoxy groups havebeen hydrolyzed; and, correspondingly, B) up to about 99.5 mole percentof at least one (meth)acrylic moiety.
 19. The interpolymer of claim 18wherein the vinylalkoxysilane is vinyltriethoxysilane.
 20. Theinterpolymer of claim 18 wherein the (meth)acrylic moiety is selectedfrom the group consisting of methyl methacrylate, butyl acrylate,methacrylic acid, and mixtures thereof.